I would say no and he or she will need a bigger tank. Eventually. What kind of box turtle do you have, and do you know how big it will get at full size? However as babies you could probably keep 2 and just upgrade to a larger terrarium , or let them loose in the house when they are big enough not to get stepped , or eaten by the family dog. Or make an outside habitat for them or on an inside screened porch if you have one you could make a great turtle pen. A man that I know keeps two box turtles in a 100 gallon terrarium but also takes them out in the yard for supervised play time. Alison

I don't know what kind she is (I'll post a picture soon), and I know she's going to eventually going to need a bigger tank. When she does get bigger, I'll let her roam around the house and outside (supervised). Just curious, why can't she be kept with a lizard with them same temperature requirements?

I wouldn't take the chance with them biting or injuring each other . a 20 gal doesn't give them the room to keep away from each other. It is just my thought process. Hopefully more people will respond that keep lizards and turtles. I used to keep turtles but they were aquatic species. I have never kept lizards but living in Fla for the last 9 years, I have a yard full of them. Cuban Brown anoles. Alison:;hi1